/*

 * Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package java.util.regex;

import java.util.Arrays;

/**

 * A lightweight hashset implementation for positive 'int'. Not safe for

 * concurrent access.

 */

class IntHashSet {

    private int[] entries;

    private int[] hashes;

    private int pos = 0;

    public IntHashSet() {

        this.entries = new int[16 << 1];      // initCapacity = 16;

        this.hashes = new int[(16 / 2) | 1];  // odd -> fewer collisions

        Arrays.fill(this.entries, -1);

        Arrays.fill(this.hashes, -1);

    }

    public boolean contains(int i) {

        int h = hashes[i % hashes.length];

        while (h != -1) {

            if (entries[h] == i)

                return true;

            h = entries[h + 1];

        }

        return false;

    }

    public void add(int i) {

        int h0 = i % hashes.length;

        int next = hashes[h0];

        //  if invoker guarantees contains(i) checked before add(i)

        //  the following check is not needed.

        int next0 = next;

        while (next0 != -1) {

            if (entries[next0 ] == i)

                return;

            next0 = entries[next0 + 1];

        }

        hashes[h0] = pos;

        entries[pos++] = i;

        entries[pos++] = next;

        if (pos == entries.length)

            expand();

    }

    public void clear() {

        Arrays.fill(this.entries, -1);

        Arrays.fill(this.hashes, -1);

        pos = 0;

    }

    private void expand() {

        int[] old = entries;

        int[] es = new int[old.length << 1];

        int hlen = (old.length / 2) | 1;

        int[] hs = new int[hlen];

        Arrays.fill(es, -1);

        Arrays.fill(hs, -1);

        for (int n = 0; n < pos;) {  // re-hashing

            int i = old[n];

            int hsh = i % hlen;

            int next = hs[hsh];

            hs[hsh] = n;

            es[n++] = i;

            es[n++] = next;

        }

        this.entries = es;

        this.hashes = hs;

    }

}